Device for simultaneously carrying out an electrochemical and a topographical near-field microscopy

ABSTRACT

A device for simultaneously carrying out an electro-chemical and a topographical near field microscopy is described, which device comprises a region for topographical near field measurement and a region for electrochemical near field measurement, with the region for topographical near field measurement extending completely as far as to the immediate tip of the arrangement, characterized in that the region for electrochemical near field measurement starts at a defined distance from the immediate tip.

This application is a U.S. national phase application under 35 U.S.C. §371 of PCT Application No. PCT/AT01/00192 filed Jun. 11, 2001, whichclaims priority to Austrian Application No. A 1012/2000 filed Jun. 9,2000.

The present invention relates to a device for simultaneously carryingout an electrochemical and a topographical near field microscopy.

The utilization of ultramicroelectrodes for the laterally resolvedcharacterization of sample surfaces provides quantitative andsemi-quantitative data on parameters such as surface activity/surfacereactivity, on the kinetics of heterogeneous as well as homogeneouselectron-transfer reactions, on corrosion processes, on the activity ofbiological components and systems (e.g. the quantitation of enzymeactivities, the study of substance transport phenomena on membranes,tissues and tissue parts, metabolic activities of individual cells, cellgroups and cell clusters, as well as organ parts and organs), and canalso be applied to the large field of the laterally resolved surfacemodification by means of etching (removal of material) or deposition(application of material).

A prerequisite for this is, however, an exact, reproducible control ofthe distance between the ultramicroelectrode and the sample in the rangeof a few electrode radii. By reacting the dissolved redox-activesubstance at the microelectrode, a diffusion-controlled current occursdue to the hemispheric diffusion to the microelectrode (FIG. 1(b)). Ifthe microelectrode is approached to the sample surface in the range of afew electrode radii, the field of diffusion is disturbed. If the samplesurface is, e.g., conductive or chemically active, the redox-activesubstance can be recycled at the sample surface, resulting in a rise ofthe Faraday current (FIG. 1(a)). If the microelectrode is approached to,e.g., a non--conductive or chemically inert sample surface in the rangeof a few electrode radii, the sample surface blocks diffusion to themicroelectrode, resulting in a reduced Farady current (FIG. 1(c)). Thissample-dependent disturbance of the field of diffusion may be describedtheoretically via diffusion equations. The numerical solution of thesedifferential equations yields the following approximation (cf. Mirkin etal., J. Electroanal. Chem., 328 (1992), 47-62):

Conductor:i _(T)(L)i _(T V)=0.68+0.78377/L+0.3315exp(−1.0672/L)Isolator:i_(T)(L)/i _(T V)=1/[0.292+1.5151/I+0.6553exp(−2.4035/L)]L=d/r  (Equation 1)with: d: distance between electrode and sample, and r: radius ofmicroelectrode.

Accordingly, for improving the sensitivity and the dynamic range, arelatively small working distance is suitable which, however, isinfluenced by the properties, such as, e.g., the conductivity or thechemcial activity. In constant height mode, this harbors the risk of acollision between the microelectrode and the sample, if the workingdistance is chosen too short (FIG. 2). Therefore, knowing the absoluteworking distance and keeping the same constant is desirable.

So far, in most applications described in the literature, the change inthe Farady current in the near field range measured on themicroelectrode is utilized for positioning (cf. Bard et al., Science,254 (1991), 68-74). By analysing the approximation curves, the distancebetween sample and microelectrode is determined. Since, however, in thereal experiment, one can neither start out with an ideal electrodegeometry (particularly if the electrodes become very small), nor from anideally parallel arrangement, the distance between ultramicroelectrodeand surface can be determined merely approximately.

Since in the conventional experiment the ultramicroelectrode does notonly follow the topographical realities, the image obtained of thesurface represents an overlaying of the influences, in particular of theelectrochemical activity and the distance between the sample surface andthe probe on the measured Faraday current at the ultramicroelectrode(FIG. 2).

With an ultramicroelectrode diameter in the range of 1-10 mm and aplanar sample, this will only mean a conditional limitation of theimaging quality. These overlaying influences, however, riseproportionally to the decrease of the (electro)-active probe area.Therefore, an image of the surface in a constant height mode is onlypossible if the distance change (e.g. by the topography of the sample)or a tilting of the sample does not exceed the allowable workingdistance.

Since a marked improvement in the resolution can only be obtained byusing smaller electrodes (<1 μm diameter), an alternative distancecontrol must be used.

First approaches to solve this problem are based on a verticalmodulation of the electrode, on the one hand, so as to allow for adifferentiation between conductive regions with a current increase andnon-conductive regions with a current decrease (cf. Wipf et al., Anal.Chem. 64 (1992), 1362-1367). By a logic circuit, the microelectrode canbe guided to follow the topography, yet not in the border regionsbetween conductive and non-conductive. On the other hand, the distancecontrol is based on convective effects which, if the probe is quicklymoved perpendicularly towards the surface, will lead to changes in thecurrent (cf. Borgwarth et al., Ber. Bunsenges. Phys. Chem. 98 (1994),1317).

Both methods are, however, still based on a current-dependent signal,and the distance between probe and sample cannot be exactly determinedfrom the approximate curves.

On the other hand, a current-independent height control based on thedetection of shearing forces (shear force mode), as has already beenused in the scanning near field optical microscopy, could besuccessfully used for the positioning of microelectrodes (Ludwig et al.,Rev. Sci. Instr. 66 (1995), 2857-2860). The basis of theshearing-force-based height control is the stimulation of themicroelectrode to horizontal oscillations in parallel to the surface bymeans of a piezo-element, and the detection of the oscillation dampingdue to hydrodynamic effects if the probe is approached to the samplesurface.

In U.S. Pat. No. 5,936,237, a combination of electromagnetic andtopographical near field microscopy is described. An electrochemicalnear field microscopy is, however—simply due to the completely differentlocal interactions on which it is based and the structural measuresinvolved for the electrochemical measurement, on the one hand, and theelectromagnetic measurement, on the other hand—not possible with thedevice described therein.

Ludwig et al. describe a current-independent height control based on anoptical detection principle. A laser beam focussed on the tip of theprobe produces a Fresnel diffraction pattern which is detected at adivided photodiode and amplified by means of a lock-in technique.

Apart from the optical method, also mechanical methods based on a smalltuning fork of piezo-electrical material which is fastened on themicroelectrode can be utilized for detection of the oscillation (Jameset al., J. Electrochem. Soc., 145 (1998), L64-L66). In this approach,the oscillation amplitude at the tip of the probe must be chosen to beso small that the electrochemical signal will not be substantiallyfalsified. This precondition simultaneously constitutes the substantiallimit for the use of ultramicroelectrodes and, thus, for an improvedlateral resolution.

Moreover, each diminishing of the microelectrode involves significantlyincreased experimental expenditures (focussing of a laser beam on sub-μmelectrode, searching for the resonance frequency etc.).

A further approach for an independent topographical recording has beendescribed by Macpherson et al. (Anal. Chem., 72 (2000), 276-285). Thisis based on the production of microelectrodes whose geometry andproperties are adapted to a cantilever. By a dynamic method, a platinumwire is symmetrically etched so that a tip forms. The wire is bent at anangle of 90°, and the vertical portion of the wire is pressed flat withthe help of metal plates. By means of an electro-deposition lacquer, themicroelectrode is electrically insulated. Due to its elasticity, theflattened portion serves for a distance control, based on the forceinteraction between sample and probe in the near field region.

With such tips and with the assistance of an AFM device, it has beenpossible to image sample surfaces, e.g. ultrafiltration membranes, incontact mode. With the approach described, electrodes having a variationwidth of the electro-active area in the μm and sub-μm-range could beproduced, in which, simplified, a hemispheric geometry was assumed andthe electro-active area was estimated with the assistance of cyclicalvoltametry.

However, the essential limits of this approach are to be seen both inthe type of sample to be examined and in the little reproducibleproduction of the electrochemical probes by the etching and insulatingprocess, as well as in the poor topographical resolution due to theundefined tip geometry, as has been demonstrated by way of the qualityof the recorded AFM images with decreasing tip size. The electrodeillustrated by Macpherson et al. also gave rise to undesired contactswith the surface to be examined, for instance, the electrode got caughtin pores of the surface. As a possible solution to this problem,Macpherson et al. proposed to use a non-contact version of this methodin that at first, in a first step, the surface to be examined istopologically scanned with the cantilever, and then in a second,separate step the electrochemical examination is carried out at theknown distance. However, this approach does not only involveconsiderably higher expenditures, but also has systematic errors, sincehysteresis effects may occur in the positioning system used for theelectrode, and already by this, an exact transmission of the topologicalinformation of a measurement process to a subsequent measurement processcannot be possible.

Publications based on a metallized cantilever in the electrochemical AFMexperiment (cf. Macpherson et al., J. Am. Chem. Soc. 118 (1996),6445-6452, Jones et al., J. Phys. Chem. B 104 (2000), 2351-2359) couldnot give a laterally resolved electrochemical information, on the onehand, since the metallized cantilever could only be manually insulatedon the glass body, and a defined microelectrode having an insulatedjacket could not be produced. The metallization served for theelectrochemical surface modification (solution behavior of a (010)potassium-hexacyanoferrate-monocrystal), the topography of which wasthen determined in situ. On the other hand, with a metallized cantilevermembranes were imaged on air which membranes were tensioned over aliquid-filled compartment such that the cantilever contacts the redoxmediator-containing electrolyte solution merely at the pore openings.Due to the measurement arrangement, thus, the pores of the membranecould be electrochemically imaged despite a lack of insulation on thecantilever, since the humidity film covering the pore openings providesthe lateral limiting (cf. Jones et al., Elechem. Commun. 1 (1999),55-60).

Therefore, it was an object of the present invention to provide a devicefor simultaneously carrying out an electrochemical and a topographicalnear field microscopy.

Furthermore, methods for characterizing surfaces shall be provided inwhich both a topological and an electrochemical information on thesurfaces to be examined are provided. Suitably, it should be possible tointegrate the measurements methods and measurement electrodes to benewly provided into already existing measuring equipment without anyconsiderable expenditures.

Further objects of the present invention comprise the provision ofelectrodes having a markedly improved measurement performance andmeasurement accuracy as compared to the prior art.

According to the invention, these objects can be achieved with a devicefor simultaneously carrying out an electrochemical and a topographicalnear field microscopy, which comprises a region for topographical nearfield measurement and a region for electrochemical near fieldmeasurement, the region for the topographical near field measurementextending, as usual, completely as far as to the immediate tip of thedevice (the probe for topographical near field measurement), with theelectrode according to the invention being characterized in that theregion for near field measurement starts at a defined distance from theimmediate tip, the region for topographic near field measurement iscovered by a conductive material except for the immediate tip, whichconductive material is covered by an insulating material except for theregion for the electrochemical near field measurement.

With the device according to the invention it has now become possible tokeep constant the distance of the region for electrochemical near fieldmeasurement from the sample over a more or less conventionaltopographical near field measurement, and thus to carry out theelectrochemical near field measurement without a systematic error causedby topological deviations of the surface.

What is essential for the device according to the invention which may beprovided with integrated or combined electrodes is that the region fornear field measurement does not extend as far as to the outermost tip ofthe device (probe) for topographic near field measurement, since thisharbors the risk of a contact with the surface as well as of a negativeinfluence on the near field measurement, but rather starts at a defineddistance from the immediate tip.

The device according to the invention now allows for a simultaneousmeasurement of both, the topology, and also of the electrochemicalproperties in the near field of a surface, in that the topology isdetermined in a manner known per se via the immediate tip of theinventive device by means of topographical near field microscopy, whileby way of this surface information, the inventive device simultaneouslyis adjusted relative to the sample such that it is located at a constantdistance from the sample surface, wherein, also simultaneously, theelectrochemical properties of the surface then are determined by thecombined, preferably integrated, region for electrochemical near fieldmeasurement. Thus, the electrochemical or chemical information can becompletely de-coupled from the topographical information, and by theprecisely defined constant distance, a non-falsified electrochemical orchemical measurement signal can be quantitatively detected incorrelation with the theoretically determined current values accordingto the solution of Fick's diffusion equation.

In the device according to the invention therefore also complex anderror-prone devices for the shearing force-based height control (e.g.according to Ludwig et al.), and piezoelectric “testing devices” (suchas, e.g., the “tuning fork” according to James et al.), respectively,are no longer required. Of course, the inventive device may, however,also be equipped with such elements, e.g. when specific experimentalquestions were to require it.

The distance which the region for near field measurement has from thethe probe tip must be such that a contact of the sample by the tip willnot result in any negative influences on the electrode. It is best ifthe dimension of the tip of the probe is adjusted such that bothmicroscopy methods can develop as optimal as possible.

For the purposes of the present application, the term “electrode” ismeant to comprise also all possible forms of ultramicroelectrodeembodiments, including sensors or actuators.

By the integration of an ultramicroelectrode with a topological scanningnear field probe, according to the invention the distance regulation ofthe integrated probe is adapted to any local, physical and chemicalinteraction between sample and inventive device in the near field. Bythis, a quantitative evaluation of the measured data is obtainedaccording to the present invention.

The topological scanning near field microscopy (e.g. atomic forcemicroscopy, AFM; scanning force microscopy, SFM) is characterized inthat the topography and surface properties is measured with a resolutionin the molecular to atomic range by surface forces between a sharp tipwhich, e.g., is fixed on a flexible lever arm (cantilever), and thesample, by deflection of the lever arm. General illustrations of varioustechniques applicable within the scope of the present invention fortopographical and electrochemical near field microscopy (scanning probemicroscopy) are shown in Bottomley (Anal. Chem. 70 (1998), 425R-475R)and in Wiesendanger (Scanning Probe Microscopy and Spectroscopy (Methodsand Application) (Ed. R. Wiesendanger), Cambridge Press (1994)), whichherewith are included as disclosure. Within the scope of the presentinvention, not only the topography of the substrate is mapped, but bythe exact distance in the near field region of the electroactive area,also a height control in the electrochemical near field measurement isenabled.

This technology by which surfaces and atoms and molecules presentthereon can be visualized with a resolution in the sub-nanometer range,is based on the work carried out by Binning et al. (Phys. Rev. Lett. 56(1986), 930-933), also described in EP 0 027 517 A. This EP 0 027 517 Aas well as those documents in which this EP-A has been cited shallherewith be included as disclosure for this technology. Various possiblebiological uses have been described, e.g. in Baselt et al. (Proc. IEEE85(4) (1997), 672-679).

In contrast to the combinations of electrochemical and topographicalscanning probe microscopy described in the prior art (Macpherson et al.,Anal. Chem. 72 (2000), 276-285), according to the invention an even moreprecise device is provided which is even easier to produce, and allowsfor electrochemical measurements which can be carried out with fewerrisks, in that the region for the electrochemical near field measurementdoes not extend as far as to the tip of the device, but ends at adefined distance behind the tip.

For the purposes of the present invention, as the “region for forcemeasurement”, or “region for electrochemical near field measurement”,respectively, that part or region of the device is to be understood atwhich the respective interaction with the surface to be examined occurs,i.e. the effect to be measured is causally taken up into the measurementdevice as a signal. For the topographical near field measurement, as arule this will be the immediate tip of a suitable AFM needle. The“region for electrochemical near field measurement” as a rule will be onthe outer side of the electrochemical near field measurement devicewhich faces the sample surface, e.g. on a metallic layer.

The defined distance to be provided according to the invention which theregion for the electrochemical near field measurement has from theimmediate probe tip which is used for topographic near fieldmeasurement, may vary within wide ranges depending on the respectiveresolution that is to be attained. According to the invention, defineddistances of the region for electrochemical near field measurement fromthe immediate probe tip ranging from 2.7 mm to 10 nm, preferably 1 mm to50 nm, in particular 0.5 mm to 100 nm, have proven particularlysuitable.

Furthermore, according to the invention by “immediate tip” that part ofthe probe or device tip is understood which is located at the outermostend of this tip and may, e.g., be only a few atoms in size. Hencefollows that according to the invention the region for electrochemicalnear field measurement, as a rule, will lie on the tip portion of, e.g.,a cantilever, yet not on the immediate tip an which the topographicalnear field measurement is carried out. If the near field interaction fortopographic imaging is based on a contact-free scanning near fieldtechnique, the region for electrochemical near field measurement mayhowever, as an exception, extend as far as to the tip.

Furthermore, according to the invention also the region by whichinformation on the topology of the surface is obtained, and the regionfor electrochemical near field measurement are rigidly positionedrelative to each other, e.g. in contrast to shearing-force-based heightcontrols and other methods in which vibration producing means(piezoelectric elements) are used to obtain such information regardingthe surface.

With the device according to the invention, not only contacting of thesensitive electrode by the surface and the measurement error involvedtherewith and mechanical risks for the combined or integrated electrodeare avoided, but also a subsequent examination of the surface (first thetopology, then the electrochemical information), as it has beensuggested as a solution to the problem by Macpherson et al., can beavoided.

Therefore, what is essential is that the region for electrochemical nearfield microscopy is created by covering the device for topographicalnear field measurement (“tip”, “cantilever”) by a conductive material.Such covering may be complete (“envelope”), yet it is also possible tocover merely certain regions of the device for topographical near fieldmeasurement (e.g. in the form of conductive tracks along thelongitudinal axis of the cantilever) with conductive material.

In case that the device for topographical near field measurement itselfis conductive (e.g. in the scanning tunneling microscope tip; “scanningtunneling microscopy” (STM); or in scanning near field opticalmicroscopy (SNOM) tips)), this conductive device itself must, of courseat-first be insulated in the device according to the invention, and onthis insulating layer, the conductive material for the electrochemicalnear field measurement must be present. In this instance, the insulatedform of the device for topographical near field measurement is (at leastpartially) covered with the conductive material so as to provide thedevice for electrochemical near field measurement which, in turn, thenmust also be insulated (with the exception of the measurement region).

This insulation of the device according to the invention is essentialsince the electrochemical near field measurement always must beperformed in a liquid medium (electrolyte; liquid, conductive phase),and accordingly, those parts of the device for the electrochemical nearfield measurement which do not serve for the immediate measurement(“measurement area”) must be protected against the liquid medium presentduring the measurement, which medium, as a rule, covers the surface tobe measured, so as to avoid any undesired influences on thismeasurement.

Preferably, the device according to the invention consists of a forcemicroscope tip which, with the exception of the immediate tip, isenveloped by conductive material, which material, except for the regionfor electrochemical near field measurement, is covered by an insulatingmaterial.

One example of such a layer assembly is illustrated in FIG. 10, wherein(1) indicates the region for topographical near field measurement, (2)indicates the region for electrochemical near field measurement, and (3)indicates the insulating material. (4) represents the connection areawhich is electrically conductively connected with the region forelectrochemical near field measurement.

The thickness of the region for the electrochemical near fieldmeasurement, or of the conductive material, respectively, will alsodepend on the respective resolution to be achieved, and the materialused, respectively. Preferably, these thicknesses will range from 10 to2000 nm, preferably from 100 to 800 nm, in particular from 150 to 500nm.

Preferably, the region for the electrochemical near field measurementconsists of a metallic element, in particular a transition metal, theuse of gold, silver, platinum, palladium, tungsten, antimony, rhodium,iridium, mercury alloys, a platinum-iridium-alloy, aplatinum-rhodium-alloy, carbon, glassy carbon, high-order pyrolyticgraphite (HOPG) being particularly preferred. Furthermore, also othermaterials, such as polysilicon, in particular doped polysilicon, metalnitrides, in particular TiN or TaN, or silicides, in particular tungstensilicide or tantalum silicide, may be used.

According to the invention, the inventive device may also be equippedwith further layers or with different layer sequences, respectively, andthus be provided with a modified electrode which is designed as amicrobiosensor, such as, e.g., an enzyme electrode, a pH-sensitiveultramicroelectrode, a potentiometric or amperometricultramicroelectrode, an ion-sensitive ultramicroelectrode, anion-selective ultramicroelectrode, a polymer-modifiedultramicroelectrode, a biomimetic ultramicroelectrode. The number andarrangement of the various regions for the electrochemical near fieldmeasurement in such a multi-electrode and multi-sensor configuration,accordingly, can be increased deliberately, by varying this layersequence and the number of layers so as to enable a multi-parametermeasurement, such as, e.g., simultaneous, electrochemical, topographicaland pH-mapping.

According to a preferred embodiment, the inventive device therefore isdesigned with electrodes configured as multi-electrodes and/ormulti-sensors, wherein preferably measurement probes designed fordifferent measurement methods are provided.

Furthermore, also several tips may be provided for topographical nearfield measurement, or several inventive combination devices may beprovided for topographical and electrochemical near field measurement inone and the same device.

Furthermore, the possibilities of using the device according to theinvention exceed those known for the electrochemical scanning microscopy(cf., e.g., U.S. Pat. No. 5,202,004 as well as U.S. Pat. No. 5,382,336,whose disclosure herewith is incorporated herein), in that now it hasbecome possible to examine any desired surface systems which are coveredby an electroactive medium.

Preferred applications of the devices according to the invention are theexamination of biochemical, biological or biomimetic coats, ofneurophysiological problems, such as cell communication, concentrationdeterminations in extracellular matrices, membrane characterizations andtransfer phenomena, electron, ion and molecule transfers at phaseinterfaces, the study of homogeneous and heterogeneous electron transferreactions, corrosion phenomena, such as, e.g., corrosion of metal andsemiconductor surfaces, the formation of corrosion/defect sites or thelike material-scientific studies, with the examination ofbiological-medical questions as well as questions in connection withsemiconductors being considered as particularly preferred.

The present invention can also be used for surface modification orsurface structuring by etching (removal of material) and/or deposition(application of material).

On the one hand, depositing as well as etching processes may be carriedout in a double-electrode arrangement, with the microelectrode acting asthe counter-electrode and the substrate acting as the working electrode.Modifications can be carried out not only in electrolyte solutions, butalso in solid ionic conductors. By applying a potential betweencounter-electrode and working electrode, reduction processes andoxidation processes, respectively, can be induced on the interfacesubstrate electrode/electrolyte, and ionic conductor, respectively, sothat deposits or etchings, respectively, in the size of themicroelectrode can be produced by the local electric field. On the otherhand, in a four-electrode arrangement, a suitable mediator can bereacted at the microelectrode which diffuses to the substrate(conductive or non-conductive), and there induces a depositing processor an etching process, respectively, by oxidation or reduction,respectively. Depositing and etching, respectively, may be performed onmetals, semimetals and alloys, moreover also polymers can be producedwhich can be prepared by electrochemical polymerisation (cf. Mandler etal., Isr. J. Chem. 36 (1996), 73-80).

Especially by the preferred layered assembly, the dimensioning of theregion for the electrochemical near field measurement can reproduciblybe diminished. Compared to the methods described in the literature whichdepart from the form of a wire, the provision of thin layers istechnically much easier and more reproducible than in case of the wireform.

The tip of the inventive device may, if necessary, be particularlyadapted to the topological examination, as is known per se for forcemicroscopy, and designed as a sensor or actuator, and have specialcoats, in particular if, e.g., special biological questions have to beaddressed.

According to other preferred embodiments, the device according to theinvention can also be designed such that a topographical near field tip,e.g. an AFM tip, carries a conductive layer insulated relative to themedium merely along one side, e.g. Furthermore, also the region forelectrochemical near field measurement may also be laterally provided,or generally other geometries may be chosen for the electrode. Thetopographical scanning measurement in contact mode just as in thetapping mode requires a sharp tip since the obtainable resolutiondepends on the radius of curvature. The integrated ultramicroelectrode,however, may preferably have the shape of a ring, a frame, a disc orhave a conical or cylindrical shape (for these geometries there alreadyexist theoretical descriptions of the current signal, except for theframe shape).

In a further aspect, the present invention also relates to a method forthe ultramicroscopic examination of surfaces, which is characterized inthat by means known per se, an inventive device is brought into thevicinity of the surface to be examined, so that both the distance to thesurface may be measured by a topographical near field technique and alsoan electrochemical near field measurement of the surface can be carriedout, and the surface is examined by moving the device over the surface,with the information obtained by the topographical near field techniquebeing directly used to keep the inventive device at approximately thesame distance from the surface so that the electrochemical near fieldmeasurement can be carried out without being impaired by topologicalfluctuations.

With this, for the first time a simultaneous electrochemical near fieldmicroscopy and a topographical near field measurement has becomepossible, which is not impaired by any systematic errors in thecorrelation of the two microscopic techniques.

Finally, the present invention also relates to a near field microscopefor the ultramicroscopic examination of surfaces, comprising

-   -   a device according to the invention,    -   an analysis unit in which the measurements made at the device        are recorded and processed,    -   means for transferring the electrochemical near field        measurement from the device to the analysis unit,    -   means for transferring the topographical near field measurement        from the tip of the device to the analysis unit, and    -   manipulation elements for the inventive device which are        controllable by the analysis unit.

This inventive near field microscope can be adapted by the personskilled in the art without difficulty on the basis of known device andmeasurement elements for the topographical near field measurement, onthe one hand, and for the electrochemical near field measurement, on theother hand, with the help of the present teaching.

Surprisingly, it has been shown that the inventive device can easily beintegrated, e.g., in AFM microscopes already on the market, and theinformation regarding the electrochemical near field measurement as wellas for carrying out the equidistant near field measurement itself can becarried out by mere handicraft steps. As a rule, the AFM apparatusalready on the market, such as, e.g., the Digital Instrument NanoscopeIII, in addition to the channels provided for the intended data recordalalso have one or further analogous input channel(s) on the dataregistering device, which allow for an additional reading-in ofmeasurement data, e.g. the electrochemical measurement data, and thecorrelation and representation with the simultaneously registeredtopographical data (cf. FIG. 4).

At the same time, the present invention also provides a simple methodfor producing the device according to the invention, in which atopographic near field microscopy probe is covered with a conductivematerial, and the conductive material is covered by an insulating layer,and the conductive material on the insulating layer is removed in theregion of the immediate tip of the probe. With the present method, notonly a suitable ultramicroelectrode which allows for electrochemicalexaminations of surfaces with a simultaneous determination of thesurface topology can be produced, but according to the invention thewell-reproducible production of these electrodes is made possible withan amazingly simple method. The method according to the invention canalso be easily included in already existing manufacturing processes,since, e.g., conventional force microscopy probes can be used as thestarting material. By the method according to the invention it isensured that the electrochemical near field measurement region of thedevice, which region is defined by the conductive material which, afterremoval of the insulating layer, is capable of accepting the signalsreceived from the sample surface, does not extend as far as to theoutermost tip of the device, but starts at a defined distance from theimmediate tip of the device (on which the interaction with the surfaces,measured for the topological imaging, occurs). In this manner, not onlythe risk of a contact of the electrochemical near field measurementdevice with the surface is prevented, but also a negative influence ofthe topological near field measurement is avoided.

What is essential to the method according to the invention is that,starting from a probe suitable for topological near field measurement,by applying and insulating a conductive material, the electrochemicalnear field measurement can be combined with the topological near fieldmeasurement in a simple manner. By removing conductive material andinsulating layer in the region of the immediate tip of the probesuitable for topographic near field measurement, not only thefunctioning ability of the tip required for the topographical near fieldmeasurement is restored again, but also a region is created with whichthe conductive material is made accessible again for measuring surfaceeffects in the electrochemical near field. The insulating layer appliedover the conductive material has the effect that the signals will onlyenter via the region which has deliberately been uncovered.

The manner in which the topological near field probe is covered with theconductive material is not critical. In general, for reasons of processtechnology, it will be preferred for the topological near field probe tobe enveloped with the conductive material. It is, however, also possibleto provide, e.g., merely one side of the probe with the conductivematerial. What is essential is only that the conductive layer issupplied from the region in which the electrochemical near fieldinteraction with the surface is to be measured, to a suitable site ofcontact in another region of the inventive device, from which site themeasurement signal can be taken.

The preferred conductive materials are either metals or they contain ametallic component, in particular a transition metal, the use of gold,silver, platinum, palladium, tungsten, and antimony. Furthermore, alsomaterials, such as polysilicon, titan nitride, rhodium, iridium, mercuryalloys, a platinum-iridium-alloy, a platinum-rhodium-alloy, carbon,glassy carbon, high-order pyrolytic graphite (HOPG) may be considered aspreferred materials. Furthermore, also other materials, such aspolysilicon, in particular doped polysilicon, metal nitrides, inparticular TiN or TaN, or silicides may be used.

The manner in which the topographical near field microscope probe iscovered with the conductive material is not critical and will depend onthe respective material to be applied. Particularly suitable methodscomprise ion sputtering, electron sputtering, chemical vapor deposition(CVD), electroless plating, electroplating and so on, in individualcases, however, also liquid phase deposition processes and spincoatingmethods are conceivable.

The covering of the layer of conductive material with the insulatinglayer preferably is effected by deposition from the gas phase, by achemical vapor deposition process, in particular, however, also by aplasma-supported CVD process, ion sputtering, electron sputtering,electroless plating, electroplating and application of insulatingpolymer layers, yet in individual cases also liquid phase depositionprocesses and spincoating methods are conceivable. With the insulationit must be ensured that the conductive material is completely covered sothat the conductive material (except for the measurement region baredlater on) does not have any contact to the electroactive medium.

The uncovering of a certain region of the conductive layer is effectedby the intentional removal of the insulating layer and the layer ofconductive material. The removal of the conductive material and/or theremoval of the insulating layer preferably are effected by a focussedion beam, optionally a neutral particle beam, by an etching process, bylaser or by focussed electromagnetic waves, removal by focussed ion beambeing particularly preferred (cf. e.g. Matsui et al., Nanotechnology 7(1996), 247-258).

The dimensioning of the layers (with which essentially the region isdefined with which the electrochemical near field defects are measured)will depend on the respective field of use and/or the resolution abilityof the inventive device, and accordingly preferably the conductivematerial will be applied in a thickness of from 10 to 2000 nm,preferably from 100 to 800 nm, in particular from 150 to 500 nm. Yetalso a monoatomic or monomolecular conductive layer is conceivable.

Preferably, the insulating layer will be applied in a thickness of from50 to 5000 nm, preferably from 100 to 2000 nm, in particular from 500 to1500 nm, and for the examination of chemically inert or non-conductivesubstrates, respectively, it must be correlated with the electroactivearea of the electrode, since the diffusion blocking in such samplesclearly depends on the area of the insulating layer (cf. Mirkin et al.,J. Electroanal. Chem. 328 (1992), 47-62).

The numerical solution of the differential equations for insulators havebeen determined with a ratio of radii of electroactive area/insulatingjacket (RG) of 10. (Cf. Kwak et al., Anal. Chem. 61 (1989), 1221-1227).However, the layer thickness must ensure a sufficient insulation of theelectroactive area and should not fall below an RG of 10, since theexperimental values then will be significantly higher than the dataobtained by simulations. Here, too, however, also monoatomic ormonomolecular layers are conceivable.

The region in which the conductive material and the insulating layer areremoved will also depend on the planned field of application of thedevice according to the invention and its measurement characteristics,respectively, and will also depend on the respective method of removingthese layers. Preferably, a region from the immediate tip as far as to adistance from the immediate tip of from 10 to 2000 nm, preferably from50 to 1000 nm, in particular from 100 to 500 nm is removed, wherein ineach individual case the particular geometry of the probe suitable fortopographical near field measurement, which geometry forms the basisfrom which it is started out with, must be taken into consideration.

Preferably, it is already provided in the inventive production methoditself that suitable connecting devices are provided at the inventivedevice for recording the measurement signals.

The invention will be explained in more detail by way of the followingexemplary embodiments as-well as drawing figures to which, however, itis not restricted.

Therein,

FIG. 1 shows calculated current-distance curves of microelectrodes whenapproaching a surface. Distance D is standardized to the radius R of theelectrode, current i_(T) is standardized to the current i_(t∞) of thenon-influenced reaction. (a) Approach to a conductive substrate. (b)Region of the non-influenced reaction. (c) Approach to an insulator;

FIG. 2 shows the dependence of the working distance on the electrodesize;

FIG. 3 shows (a) the schematic illustration of the distance control viathe optic detection method and the diffusion limitation in the nearfield range by an insulating or chemically inert sample surface;

-   -   (b) the schematic illustration of the distance control via the        optic detection method and recycling of the electroactive        substance in the near field range by a conductive or chemically        active sample surface;

FIG. 4 shows a schematic illustration of the measurement assembly if theinventive near field probe is based on an AFM cantilever;

FIG. 5 shows a cyclical voltammogram of an insulated near field probe200 nm gold, 800 nm insulation, taken up in 5 mM K₄[Fe(CN)₆]/0.1 M KCl;advance speed 100 mV/s.

FIG. 6 shows a cyclical voltammogram of an integrated electrochemicalnear field probe 100 nm gold, 800 nm insulation, taken up in 5 mMK₄[Fe(CN)₆]/0.1 M KCl; advance speed: 100 mV/s;

FIG. 7 shows (a) a schematic illustration of an exemplary AFM cantileverafter application of an electroactive layer and an insulating layer;

-   -   (b) the AFM image of a gold-GaAS-grid with a periodicity of 3.4        μm with a commercial Si₃N₄ cantilever in contact mode;    -   (c) the AFM image of the gold-GaAS grid with a periodicity of        3.4 μm with the inventive metal-coated (200 nm gold) and        insulated (800 nm nitride) AFM cantilever in contact mode;

FIG. 8 shows (a) a schematic illustration of the exemplary AFMcantilever after the first two milling steps;

-   -   (b) the AFM image of a p-doped silicon surface after deposition        of octadodecyl siloxane islands, imaged with a commercial Si₃N₄        cantilever in the contact mode (imaging grid 10×10 μm) island        size ˜1-2 μm, height ˜2.6 nm.    -   (c) the AFM image of the octadecyl siloxane islands in the        contact mode (image grid 10×10 μm) with the inventive modified        probe (200 nm gold, 800 nm insulation layer, radius of curvature        ˜300 nm, height ˜2 μm (production step FIG. 13 a)).    -   (d) an image of 300 nm gold dots on a GaAS substrate with a        commercial Si₃N₄ cantilever, in the contact mode.    -   (e) an image of 300 nm gold dots on a GaAs substrate in the        contact mode with the inventive modified probe (200 nm gold, 800        nm insulation layer, radius of curvature ˜300 nm, height 2 μm;        and

FIG. 9 shows (a) a schematic illustration of an inventive scan nearfield probe with an integrated ultramicroelectrode based on an AFMcantilever.

-   -   (b) the AFM image of a gold-gaAS grid with a periodicity of 3.4        μm with a commercial Si₃N₄ cantilever in the contact mode on        air. (c) the AFM image of the gold-GaAS grid with a periodicity        of 3.4 μm in the contact mode with an inventive scan near field        probe with integrated ultramicroelectrode (tip height ˜1 μm).

FIG. 10 shows a principle outline of the device according to theinvention in schematic cross-section (a) and in a schematic perspectiveview (b);

FIG. 11 shows a principle outline to describe a production method forthe device according to the invention;

FIG. 12 shows a principle outline to describe the production method forthe device according to the invention in a view on the side face (a) andon the end face (b);

FIG. 13 shows a principle outline to describe the production method ofthe device according to the invention;

FIG. 14 shows a principle outline for the production method of thedevice according to the invention;

FIG. 15 shows a principle outline to describe the production method forthe device according to the invention in multielectrode form; and

FIG. 16 shows a principle outline for the inventive multielectrodescomprising an electrically conductive measurement tip;

FIG. 17 shows an embodiment having several individual tips arranged inparallel on a base body;

FIG. 18 shows an embodiment in form of a tip array;

FIG. 19 shows a schematic illustration of individual and multipleintegrated frame/annular micro/nanoelectrodes; and

FIG. 20 shows a combined AFM-SECM measurement with the measurementarrangement according to the invention.

EXAMPLES Example 1

Production of the Near Field Probe with Integrated Ultramicroelectrode

For the production, in the first step the cantilever and the glass bodyare coated with any desired electrode material, such as, e.g., gold. Byusing different coating times, the thickness of the electrode layer canbe variably and reproducibly be made. By the plurality of the electrodematerials available, the desired properties of the ultramicroelectrodecan be adjusted, such as, e.g., the use of an antimonyultramicroelectrode for pH-sensitive measurements.

To electrically insulate the (electro)active area, the now coatedcantilever is modified, e.g. with a silicon nitride layer. Theapplication of the insulating layer is effected e.g. by aid of aplasma-enhanced chemical vapor deposition at a temperature of e.g. 300°C. and a gas mixture of SiH₄ and NH₃ in the pressure range of a few Torrand in the power range of a few 10 W power. The insulation may envelopethe cantilever, yet it must at least completely insulate the conductivelayer and during the measurements in liquid media it must be resistantto the solutions used. By using different coating times, the layerthickness of the nitride layer and thus, the degree of insulation can befixed.

The uncovering of the (electro)active area is effected by methods ofmicrostructur technology, such as, e.g., the focussed ion beam (FIB)technique. The tip of the cantilever can be milled such that a planarultramicroelectrode, such as, e.g., a frame microelectrode, is produced.In the middle of this annular electrode, the original scanning nearfield tip is etched with the help of the FIB technique so that it willhave a small, defined radius of curvature for the topographic imaging.

The length of the distance tip is now varied in correlation to theultramicroelectrode radius so that the distance of theultramicroelectrode will be in the sensitive working range to the sample(cf. FIG. 1). Since the working distance may fall below the radius ofthe microelectrode due to the controlled distance regulation, a furtherimprovement of the resolution is attained (FIG. 3).

As an exemplary embodiment, the integrated scanning near field probeproduced according to the invention, with an integratedultramicroelectrode was installed in an AFM (FIG. 4).

For a near field probe according to the invention with a conductivecore, the method described for a nonconductive core also appliesaccordingly, with the following modifications:

-   (i) applying an insulator layer on the conductive core;-   (ii) applying a conductive layer;-   (iii) applying an insulator layer once more;-   (iv) uncovering again the original tip by means of a    material-removing method.

For a near field probe according to the invention comprising alight-conductive core, such as, e.g., a fiber-optical light guide, themethod described for a non-conductive core applies accordingly with thefollowing modifications:

-   (i) applying a conductive layer;-   (ii) applying an insulating layer;-   (iii) uncovering the original tip again by means of a    material-removing method.

The electrochemical properties of the scanning near field probesaccording to the invention and their applicability for localcharacterization as well as the quality of the individual manufacturingsteps can be examined by electrochemical methods, such as, e.g., thecyclical voltammetry.

This is shown by way of example on an Si₃N₄ cantilever modified with 200nm gold and an insulating layer of 800 nm Si₃N₄. At a mediatorconcentration of 10 mM in 0.1 M of potassium chloride, thecyclovoltammogram of the modified cantilever shows a leakage current of<1 pA (FIG. 5). Assuming that this is due to pinholes in the insulation,with the help of the theory of the stationary limiting current (I_(T∞)):I_(T∞)=4nFcDr  (Equation 2),with: n: number of transmitted electrons, F: Faraday constant, D:diffusion coefficient, c: concentration, r: radius of the diskmicroelectrode, an (electro)active area of <0.01 nm² was determined on adisk electrode.

By way of example, by means of an integrated ultramicroelectrode in anon-conductive scanning near field probe having an (electro)activedimension of 100 nm diameter and an edge length of 2 μm, the theoreticaldiffusion limiting current is compared with the experimental data. Withthe help of equation 1, the diffusion limiting current of amicro-annular electrode can be correlated with the geometrical factorsof the electrode, if a/b>0.9 (cf. W. R. Smythe, J. Appl. Phys., 22, 1499(1951)): $\begin{matrix}\begin{matrix}{I_{d} = {nFDcl}_{o}} \\{I_{o} = \frac{\pi^{2}\left( {a + b} \right)}{{In}\left\lbrack {16{\left( {a + b} \right)/\left( {b - a} \right)}} \right\rbrack}}\end{matrix} & \left( {{Equation}\quad 3} \right)\end{matrix}$with: n: number of transmitted electrons, F: Faraday constant, D:diffusion coefficient, c: concentration, I: geometric factor of theannular microelectrode, a: inner radius, b: outer radius of the annularmicroelectrode.

For annular microelectrodes having any desired ratio of the inner to theouter radius of the electrode, the parameter I_(o) can be described asfollows (cf. A. Szabo, J. Phys. Chem., 91, 3108 (1987)): $\begin{matrix}{I_{o} = \frac{\pi^{2}\left( {a + b} \right)}{{In}\left\lbrack {{32{a\left( {b - a} \right)}} + {\exp\left( {\pi^{2}/4} \right\rbrack}} \right.}} & \left( {{Equation}\quad 4} \right)\end{matrix}$

Assuming that the theoretical determination of the diffusion limitingcurrent for annular microelectrodes also can be applied to thisgeometry, with a diffusion coefficient for potassium hexacyanoferrate(II) of 6.7 10⁻⁶ cm²/s for an inner radius of 0.95 μm and an outerradius of 1.1 μm, there results a diffusion limiting current of ˜0.12 nAat a concentration of the redox mediator of c=5 mM. As is apparent fromFIG. 6, the value calculated with the help of the dimensions of theannular microelectrode is in sufficient agreement with the measuredvalue from the cyclovoltammogram, taking into consideration e.g.phenomenas, such as surface roughness and edge effects of theultramicroelectrode. Since, in contrast to the approach by Macpherson etal., this is a planar microelectrode geometry, comparative statementsregarding the dimensions of the (electro) active area can be made withthe help of, e.g., the electron microscopy.

A prerequisite for the use of such integrated ultramicroelectrodes forcharacterizing surfaces is that the modification of the scanning nearfield tip does not impair the detection within the scope of the physicalmeasurement principle. Therefore, AFM measurements were carried out withmodified probes in air in the contact mode as an example. As thesamples, both nearly planar structures of self-organizing monolayers onp-doped silicon platelets and also three-dimensional semiconductorstructures were examined. The examination aimed at documenting theinfluence of the coating on the responding behavior of the cantilever(FIG. 7). By applying the conductive and the insulating layers, thegeometry of the topographical imaging tip changes on account of thelayer thicknesses. The original radius of curvature increasessignificantly. This can be shown by way of the image e.g. of a gold-GaAsgrid having a periodicity of 3.4 mm. Since, however, in the methodaccording to the invention, the original tip has been made by milling,this does not constitute a limitation of the method for the imagingquality of the scanning near field probe with integratedultramicroelectrode.

The stability of the coatings applied was tested by way of AFMmeasurements in the contact mode (FIG. 8). This image shows by way ofexample the topography of polysiloxane islands on a p-doped siliconsurface which had been recorded with a probe produced according to theinvention. The measurement tip had a height of 2 μm and a radius ofcurvature of 300 nm. This is recognizable when compared with anon-modified AFM tip.

The stability of the ultramicroelectrode according to the invention wasalso shown by way of a gold-GaAS grid having a periodicity of 3.4 μm(FIG. 9).

For the use of force interactions between near field probe andmechanically instable samples, such as, e.g., in the examination ofbiological systems, a dynamic mode must be chosen for mapping thetopography of the sample. In the tapping mode (dynamic mode,intermittent contact mode), the cantilever is stimulated with highfrequency—in solution in a range of from 20 to 40 KHz—to an oscillationnear the resonance frequency, and contacts the sample only at the pointof the maximum amplitude of oscillation. In a first approximation, theoscillating cantilever can be described as a harmonic oscillator. Themodulation of the scanning near field probe produces a modulation of theelectrochemical measurement signal with the same frequency. By asuitable data recording and processing of the electrochemicalmeasurement signal, the contribution produced by the oscillation of thescanning near field probe can be determined as a mean.

In the measurement tip according to the invention, the measurement tip(i) which serves to map the surface topography consists of Si₃N₄, yet bythe present method it may also be produced of any material. Height andshape of the measurement tip can be varied. Typical dimensions—withoutrestriction of the generality—are a height of 0.2 μm at a radius ofcurvature of the tips of <30 nm.

The geometry of the ultramicroelectrode may be controlledly varied interms of shape and size. The distance of the electrode to the samplesurface is adjusted by the height of the above-described measurement tip(i).

An insulating cover layer (iii), e.g. silicon nitride, covers the entireprobe with the exception of the ultramicroelectrode, the connectionarea, and the measurement tip, and in the measurement tip according tothe invention, this is, e.g. a nitride layer of a thickness of 900 nmwhich, preferably is applied by means of CVD. However, also any otherinsulation layer is possible which meets the requirements regardinginsulation, flexibility and resistance to the media used during themeasurement. This insulation layer must be sufficiently thick so as toguarantee the insulation, and sufficiently thin so as not to restrictthe dynamic properties of the measurement tip.

Size and geometry (circular, elliptic, rectangular and also irregularelectrode areas) of the electrically active area of theultramicroelectrode can be produced and varied in controlled manner,just like the distance of the ultramicroelectrode from the surface andthe relation of this distance to the electrically active area of theultramicroelectrode.

The electrode jacket (insulating layer) is electrically insulating andchemically inert relative to the solutions used during measurement inliquid media.

The probe may advantageously be produced by the method according to theinvention, as is described in more detail in the following. Theproduction method illustrated in the enclosed principle outlines (FIGS.11 to 14) substantially comprises the following steps:

The device according to the invention (probe) with an integratedultramicroelectrode, in the examplary embodiment is based on base bodyat first in the form of an Si₃N₄ cantilever (FIG. 11(1)). Onto thelatter, a conductive layer is applied, in the exemplary embodiment 200nm of gold are sputtered thereon. The electrically conductive layer iscovered with an insulating layer which must be resistant to thesolutions used during measurements in liquid media (FIG. 11(3)). In themeasurement tip according to the invention, e.g. a silicon nitride layerhaving a thickness of 900 nm has been deposited, e.g. by means of aplasma-supported CVD process.

In the next step, the outer insulating layer covering the electrode anda part of the electrode and of the base body is locally removed (regionsindicated in broken lines in FIG. 12) by means of a material-removingmethod, preferably with a focussed ion beam arrangement, as illustratedin FIG. 12. This process is carried out once, from the side face (FIG.12 a) and once, offset by 90° thereto, from the end face (FIG. 12 b).

From the remaining cuboid with the pyramid put thereupon and having thematerial sequence insulator-metal-insulator, a new measurement tip isformed, preferably by means of the focussed ion beam device as in theprevious method step, by removing the regions indicated in broken linesin FIG. 13, once from the side face and once from the end face.

According to the invention, the measurement tip may be formed by asuitable selection of the material removal from the material of the basebody (FIG. 13 a), the conductive layer (FIG. 13 b) or the insulatinglayer covering the metal (FIG. 13 c). Illustrations d, e and f in FIG.13 show the resultant tip configurations.

The height of the tip, the radius of the tip and the shape of the tipcan also be varied by a suitable selection of the material removal. Inthe exemplary embodiment, the measurement tip consists of the materialof the cantilever used.

Finally, the electrode areas in the exemplary embodiment are cleanedfrom re-deposited material by a special form of material removal withthe FIB (single pass mill). In this single pass mill, thematerial-removing ion beam scans the regions indicated in FIG. 14 inbroken lines just once, from top to bottom, so that finally the samplesurface is sputtered by the ion beam just once and re-deposited materialis removed thereby.

According to the invention, however, any other method that cleans thesurface while maintaining the structure, such as, e.g., an etchingprocess, may be used for cleaning the electrode areas.

Contacting the ultramicroelectrode may take place at any point desired,by locally removing the uppermost insulating layer by a structuringmethod and baring a respective connecting contact to the conductivelayer.

In the above exemplary embodiment, contacting of the ultramicroelectrodeis effected at the rear end of the glass body of the cantilever (FIG.10).

From the method according to the invention, there result, e.g., thefollowing possibilities of varying the electrode area or geometry, orthe ratio of electrode area to the distance of the electrode from thesample surface and the lateral distance of the electrode from themeasurement tip:

-   1. By applying electrically conductive layers of different    thicknesses, the electrically active area of the probe can be varied    independently of the pedestal height entered in FIG. 12.-   2. With a fixed thickness of the electrically conductive layer, as    is the case in the exemplary embodiment, with a pyramidal base body,    the electrode areas can be diminished for greater pedestal heights    (FIG. 12).-   3. The geometry of the electrode can be varied by the choice of the    base body on which the electrically conductive layer is applied. In    the exemplary embodiment, a cantilever was used with whose pyramidal    tip a square frame electrode results—as is apparent from FIG. 10.    According to the invention, however, a base body of any desired    shape may be used as the starting material, and thus, e.g.,    circular, elliptic, rectangular or polygonal electrodes can be    realized. With the focussed ion beam device used in the exemplary    embodiment, just as in any suitable structuring method, any    desired—also irregular—shape of the base body can be provided,    whereby it becomes possible to realize non-closed, in particular    also segmented, ultramicroelectrodes.-   4. The ratio electrode area/distance of the electrode to the sample    surface can be varied by adjusting the height of the measurement    tip.-   5. The lateral distance of the microelectrode from the measurement    tip for determining the surface topology may, as in the exemplary    embodiment, be determined by the pedestal height (FIG. 12), with the    base body having an appropriate shape.

In terms of number of layers and sequence of layers, the methodaccording to the invention is not limited in any way. By an alternatingcoating of the insulating base body with conductive and insulatinglayers and, analogous to the exemplary embodiment, subsequent localremoval of the material, thus also multielectrodes can be produced. Thedistances of the individual electrodes to the sample surface may vary.As an example, FIG. 15 shows an exemplary embodiment for a doubleelectrode. For a probe according to the invention comprising severalintegrated electrodes, the method described will apply accordingly, withthe modification that the material-removing step can be carried outtwice with different pedestal heights (FIG. 15). The production of themeasurement tip proper and the removal of redeposited material from theelectrode are carried out analogously to the above-described exemplaryembodiment.

If an electrically conductive material is used as the base body, adouble electrode will be obtained by a series of structuring depositingand etching steps, with the measurement tip itself now beingelectrically conductive (FIG. 16).

In this case, any desired multilayer systems can be built up and thus,multielectrodes can be realized.

Any material may be used as the base body of the probe, in particularalso fiber-optic guides and, generally, wave guides for electromagneticwaves. In this instance, e.g., a light beam (general electromagneticwaves) can be guided as far as to the probe tip and onto the sample.Moreover, also an external jacket layer may in this way be used as awave guide or as a fiber-optic wave guide.

A further embodiment for the measurement methodology is possible bycombining several measurement probes. This may be effected in the formof several individual tips arranged in parallel on a base body (FIG. 17)or in the form of an array of tips (FIG. 18).

In this instance, a plurality of measurement probes analyse in parallelindividual regions of the sample, from which the total image of thesample surface can be provided by means of a data processing program.Depending on the number of measurement probes used, this will lead to ashortening of the measurement duration. A further variant is thesimultaneous use of measurement probes of various types. For instance,ultramicroelectrodes having different electrode areas or electrodeshapes, or also electrodes made of different materials ormultielectrodes could simultaneously be used. Moreover, also thecombination of measurement tips serving as microbiosensor, pH-sensitiveor potentiometric ultramicroelectrode is possible, or ion-sensitive orion-selective ultramicroelectrodes or any other near field microscopicanalysis method can be combined with each other. When a signal is takenin case of a combination of measurement probes as illustrated in FIG.17, care must be taken that such measurement probes are guided mutuallydecoupled. The taking of the measurement signal of each individual tipof a multielectrode array may, e.g., be effected via electrical linesguided on the webs of the array.

In FIG. 17, (1) denotes the base body with three integratedultramicroelectrodes, (2) denotes the contact areas for signal taking,and (3) denotes the electrical parting line. In FIG. 18, (1) denotes anultramicroelectrode array, (2) an individual multielectrode (may be of adifferent type), and (3) the webs of the multielectrode array.

In FIG. 19, a schematic illustration of individual and multipleintegrated frame/annular micro/nanoelectrodes is given: (a) schematicsectional representation of an AFM cantilever after integration of theelectrode and processing of the AFM tip; (b) integratedframe-micro/nano-electrode; (c) integrated annular micro/nano-electrode;(d) multiple integrated frame-micro/nano-electrodes; (e) multipleintegrated annular micro/nano-electrodes. In FIG. 19, (1) denotes anintegrated frame/annular micro/nano-electrode, (2) processed AFM tip,(3) electrical contact for signal taking, (4) conductive layer (e.g.gold), (5) electrically insulating layer, (6) original, untreated AFMcantilever and (7) multiple integrated frame/annularmicro/nano-electrodes.

Example 2

Combined AFM-SECM Measurement with the Measurement Arrangement Accordingto the Invention.

The combined measurement tip according to the invention was installedinto a scanning force microscope from Digital (Nanoscope III). By way ofexample, gold webs on a gallium-arsenide wafer were examined. The goldwebs have a periodicity of 4.3 μm and a height of 0.2 μm. Themeasurement was carried out in 0.5 mol/l KCl with a portion of 0.01mol/l [Fe(CN)₆]⁴⁻. The integrated annular gold electrode used in thisexample had an inner diameter of 900 nm. The shaped AFM tip was producedwith a length of 1.5 μm.

Measurement parameters: imaging area 20 μm×20 μm; scan rate: 2 Hz; themeasurement tip combined according to the invention was scanned from theleft towards the right and from the top towards the bottom. The resultis illustrated in FIG. 20: (left-hand side) topographic image of thesurface with the AFM tip; (right-hand side) simultaneously recordedelectrochemical image with the integrated electrode. A constantpotential of +0.6 V (against an AgQRE (silver quasi-referenceelectrode)) was applied to the electrode.

1. A device capable of simultaneously carrying out electrochemical nearfield measurement and topographical near field measurement during use,the device comprising an arrangement comprising a region adapted fortopographical near field measurement and a region for electrochemicalnear field measurement, wherein: the region for topographical near fieldmeasurement extends completely to an immediate tip of the arrangement;the region for electrochemical near field measurement starts a defineddistance from the immediate tip; the region for topographical near fieldmeasurement is covered by a conductive material except for the immediatetip; and conductive material is covered by an insulating material exceptfor the region for the electrochemical near field measurement.
 2. Thedevice of claim 1, further defined as comprising a scanning near fieldtip, which device, except for the immediate tip, is enveloped by aconductive material, which conductive material, with the exception ofthe region for electrochemical near field measurement, is covered by aninsulating material.
 3. The device of claim 1, wherein the region forelectrochemical near field measurement has a thickness of from 10 to2000 nm.
 4. The device of claim 3, wherein the region forelectrochemical near field measurement has a thickness of from 100 to800 nm.
 5. The device of claim 4, wherein the region for electrochemicalnear field measurement has a thickness of from 150 to 500 nm.
 6. Thedevice of claim 1, wherein the region for electrochemical near fieldmeasurement is comprised of a metal or metal alloy.
 7. The device ofclaim 6, wherein the region for electrochemical near field measurementis comprised of gold, silver, platinum, palladium, tungsten, cadmium,aluminum, rhodium, iridium, copper, mercury alloys, aplatinum-iridium-alloy, a platinum-rhodium-alloy, carbon, carbonelectrode-glassy carbon, a high-order pyrolytic graphite (HOPG), apolysilicon, a doped polysilicon, a metal nitride, or a silicide.
 8. Thedevice of claim 7, wherein the region for electrochemical near fieldmeasurement is comprised of a metal nitride further defined as TiN orTaN.
 9. The device of claim 8, wherein the conductive material iscomprised of a silicide further defined as tungsten silicide or tantalumsilicide.
 10. The device of claim 1, further defined as amicrobiosensor.
 11. The device of claim 10, wherein the microbiosensoris further defined as an enzyme electrode, a pH-sensitiveultramicroelectrode, a potentiometric ultramicroelectrode, anion-sensitive ultramicroelectrode, an ion-selective ultramicroelectrode,a potentiometric ultramicroelectrode, amperometric ultramicroelectrode,and/or a biomimetic ultramicroelectrode.
 12. The device of claim 1,further defined as comprising a plurality of electrodes configured asmultielectrodes and/or multisensors.
 13. The device of claim 12, whereinmeasurement probes adapted for different measurement methods areprovided.
 14. The device of claim 1, wherein the defined distance of theregion for near field measurement from the immediate tip is 0.5 μm to100 nm.
 15. The device of claim 14, wherein the defined distance of theregion for near field measurement from the immediate tip is 1 μm to 50nm.
 16. The device of claim 15, wherein the defined distance of theregion for near field measurement from the immediate tip is 2 μm to 30nm.
 17. A method for the ultramicroscopic examination of a surfacecomprising: obtaining a device capable of simultaneously carrying out anelectrochemical and a topographical near field microscopy during use,the device comprising an arrangement comprising a region adapted fortopographical near field measurement and a region for electrochemicalnear field measurement, wherein: the region for topographical near fieldmeasurement extends completely to an immediate tip of the arrangement;the region for electrochemical near field measurement starts a defineddistance from the immediate tip; the region for topographical near fieldmeasurement is covered by a conductive material except for the immediatetip; and conductive material is covered by an insulating material exceptfor the region for the electrochemical near field measurement; bringingthe device into the vicinity of the surface to be examined so that botha distance to the surface can be measured by a topographical near fieldtechnique and also an electrochemical near field measurement of thesurface can be carried out; and examining the surface by moving thedevice over the surface, with information obtained by the topographicalnear field technique being used to keep the device approximately at thesame distance to the surface so that the electrochemical near fieldmeasurement is not impaired by topological fluctuations.
 18. A nearfield microscope comprising: a device capable of simultaneously carryingout an electrochemical and a topographical near field microscopy duringuse, the device comprising an arrangement comprising a region adaptedfor topographical near field measurement and a region forelectrochemical near field measurement, wherein: the region fortopographical near field measurement extends completely to an immediatetip of the arrangement; the region for electrochemical near fieldmeasurement starts a defined distance from the immediate tip; the regionfor topographical near field measurement is covered by a conductivematerial except for the immediate tip; and conductive material iscovered by an insulating material except for the region for theelectrochemical near field measurement; an analysis unit in whichmeasurements made by the device are recorded and processed during use;the microscope adapted to transfer the electrochemical near fieldmeasurement from the device to the analysis unit and the topologicalnear field measurement from the tip of the device to the analysis unitduring use; and manipulating elements for the device that arecontrollable by the analysis unit during use.
 19. The near fieldmicroscope of claim 18, further defined as comprising a forcemicroscope.